1. Field of the Invention
This invention lies in the field of apparatus for pumping liquids from deep boreholes, such as deep water or oil wells. More particularly, it concerns a type of deep well pump in which a continuously driven hydraulic pump at the surface provides motive power to drive a down hole reciprocating pump in which one cylinder and piston provides the force to drive a second piston in a smaller cylinder to pump liquid up the tubing.
Still more particularly this invention relates to a method by which a high pressure accumulator acts as a storage of energy during the second part of the pumping cycle in which liquid is not lifted from the borehole, and the accumulator applies its stored energy to aid the surface pump in the first part of the pumping cycle in which liquid is lifted from the borehole.
2. Description of the Prior Art
In the prior art there are instances where hydraulic pumps have been placed in a deep borehole, hung on tubing, in which a hydraulic pump at the surface supplied pressurized liquid to the down hole pump in order to pump well liquids up the tubing. Unlike the situation in the case where sucker rod pumps are used with surface mechanical pumping equipment in which a mechanical counterbalance can be utilized to average out the irregular pumping force required in the two-part pumping cycle, in which the sucker rods are lowered and then lifted, carrying the pumped liquid, the hydraulic systems in the prior art have not utilized a counterbalance equivalent. This causes a highly variable pumping force requirement and necessitates a larger size of engine to drive the system. The counterbalance in this instance is provided with a high pressure hydraulic accumulator which accepts and stores energy during the part of the pumping cycle in which little energy is required from the surface pump, and on the next part of the cycle, delivers the stored energy to assist the surface pump.